Science

Study: More GMOs Means More Pesticides

Genetically modified soybeans are resistant to the weed-killer, Roundup.

Use of weed killers has gone up since farmers began planting genetically-modified crops, according to a study that lays most of the blame on herbicide-resistant weeds.

Corn, soybeans and cotton that are genetically engineered to survive doses of the herbicide glyphosate were supposed to reduce the amount of chemicals farmers used. But Charles Benbrook of Washington State University says that strategy backfired.

"In the first years, the technology worked beautifully. But by over-using it, we've really undermined the basic effectiveness of it," he said.

That's because weeds evolved to be more chemical-resistant, too. Benbrook found that between 1996 -- when genetically engineered crops were introduced -- and 2011, herbicide use has gone up by 527 million pounds. Insecticide use has dropped by 123 million pounds. Benbrook's article was published in the journal, Environmental Sciences Europe.

"To manage the weeds, farmers are having to apply one or two additional herbicides, including more and more acres treated with older, higher-risk products," he said. Benbrook says glyphosate, which is sold by Monsanto under the name Roundup, is generally regarded as one of the safer herbicides.

The problem is most prevalent in parts of the country like the cornbelt, where farmers tend to grow a single crop. In California, the wide diversity of crops has insulated farmers so far.

"I did not spray any pesticides on the cotton this year at all," said Fresno County farmer Paul Betancourt. "I've long had this theory that the healthier plants are, the less pesticide and the less herbicide you gotta use."

Martina Newell-McGloughlin, the director of the International Biotechnology Program at UC Davis, said the paper missed the "big picture."

"The really big thing from the herbicide-tolerant perspective is that it allows you to manage weeds so much better so that farmers can switch to no-till agriculture, which is so much healthier for the soil and the environment," she said.

A spokesman from Monsanto said in an email, "We are aware of the study and will review it thoroughly, as we do all studies that relate to our products and technologies."